Round Robin Testing: Exploring Experimental Uncertainties through a Multifacility Comparison of a Hinged Raft Wave Energy Converter

The EU H2020 MaRINET2 project has a goal to improve the quality, robustness and accuracy of physical modelling and associated testing practices for the offshore renewable energy sector. To support this aim, a round robin scale physical modelling test programme was conducted to deploy a common wave energy converter at four wave basins operated by MaRINET2 partners. Test campaigns were conducted at each facility to a common specification and test matrix, providing the unique opportunity for intercomparison between facilities and working practices. A nonproprietary hinged raft, with a nominal scale of 1:25, was tested under a set of 12 irregular sea states. This allowed for an assessment of power output, hinge angles, mooring loads, and six-degree-of-freedom motions. The key outcome to be concluded from the results is that the facilities performed consistently, with the majority of variation linked to differences in sea state calibration. A variation of 5–10% in mean power was typical and was consistent with the variability observed in the measured significant wave heights. The tank depth (which varied from 2–5 m) showed remarkably little influence on the results, although it is noted that these tests used an aerial mooring system with the geometry unaffected by the tank depth. Similar good agreement was seen in the heave, surge, pitch and hinge angle responses. In order to maintain and improve the consistency across laboratories, we make recommendations on characterising and calibrating the tank environment and stress the importance of the device–facility physical interface (the aerial mooring in this case).</jats:p

Using Underwater Imagery as a Complementary Tool for Benthos Sampling in an Area with High-Energy Hydrodynamic Conditions

International audienceUnderwater imagery is increasingly being used in the description of communities and habitats, as a tool to aid in the designation and management of marine protected areas. Here, we developed an underwater imagery system to monitor the seafloor and benthic communities in the Raz Blanchard (Aldernez Race), an area in the English Channel characterized by high-energy hydrodynamics. Despite the difficult conditions of acquisition, the underwater images highlighted the heterogeneous nature of the seabed in the Raz Blanchard. In this way, underwater imagery is a useful tool in providing additional information to standard benthic observations, particularly for the description of sessile epifauna and benthic landscapes. This system is flexible, robust and simple enough to be used in coastal and offshore areas, and is suitable as a complementary tool in benthic surveys to monitor the status and changing trends of seabed fauna and could be applied in future surveys

Suspended sediment concentration in relation to the passage of a tidal bore (See River estuary, Mont Saint Michel Bay, NW France)

International audienc

Influence du plan de pose sur les distributions de porosité au sein d'une carapace de digue à talus

National audienceLa pose de blocs artificiels nécessite une étude économique prenant en compte, d'une part, l'accroissement du coût de construction de la digue en raison du grand nombre de blocs qui doivent être utilisés et, d'autre part, l'augmentation des coûts de pose et de réparation de la digue dus aux contraintes associées au placement de blocs élancés et/ou fortement imbriqués. La méthode de pose est un paramètre important qui influence la densité de pose des blocs par unité de surface, et donc la porosité surfacique et volumique de la carapace, conséquences sur la stabilité. Dans ce papier, nous présentons deux manières différentes de considérer les porosités au sein de la carapace et ainsi d'examiner l'évaluation de ce paramètre en termes de "performances hydrauliques" et "stabilité". Si la porosité volumique est relativement aisée à déterminer en modèle physique, ce n’est pas le cas de la porosité surfacique. C’est pourquoi nous avons opté pour une représentation virtuelle en trois dimensions à l'aide d'un logiciel DAO. Cette analyse aide à mieux comprendre l'influence de la porosité sur les phénomènes hydrauliques au sein de la carapace et donc les conséquences sur la stabilité globale de l’ouvrage de défense

Porosity effect on the hydraulic stability of armour unit

International audienc

Hydraulic stability and wave overtopping of Starbloc ® armored mound breakwaters

(IF 2.73; Q1)International audienceThe new interlocking concrete armour unit, 'Starbloc ® ', has been developed for coastal protection purposes. This compact armour unit consists of three 'legs' and two 'noses'. The design is based on finding an optimized placement on the slope with at least three contacts, which is self-stable under the own unit weight. 'Shipshape placement' on a single layer is recommended on steep slopes like 3V: 4H. 2D hydraulic model tests are performed to investigate the hydraulic stability and hydraulic performance of this new unit. The model tests are performed with irregular waves to observe the behaviour of the structure, applying JONSWAP spectrum with a peak enhancement factor γ ¼ 3.3. Based on hydraulic model tests, the results demonstrate a high hydraulic stability for the interlocked individual units (N s ¼ 2.9), despite of a satisfactory level of overtopping performance (γ r ¼ 0.45). Global damage (extraction of group of units) on very dense armour placement highlights the importance of considering a minimum porosity, 34%, inside the armour layer (surface) instead of a mean value (volume)

Experimental Study to Determine Forces Acting on Starbloc Armor Units and Velocities Occurring in a Single-Layer Rubble Mound Breakwater under Regular Waves

International audienc

Influence of the tidal bore on sediment transport in the Mont-Saint-Michel estuary, NW France

The Mont Saint Michel estuary is a megatidal setting (tidal range up to 14 m). It is characterized by a strong tidal asymmetry during spring tides, with the flood stage much shorter and quicker than the ebb, reaching commonly a velocity of 2m/s into the estuarine channels. In estuaries with tidal ranges greater than 6 m, the difference of elevation between the rising tide and the river creates a discontinuity of velocity and pressure, called tidal bore (or "mascaret" in French). Visually, a tidal bore can be described as a wave or series of waves propagating upstream. This study takes place into a national project "ANR Mascaret". Part of the field work we performed recently on the tidal bores that propagate into the Mt St Michel estuary, aims in studying the impact of the bore fluid dynamics on sediment transport. This is an important issue for a better understanding of the complex fluid-sediment interactions and for the operation of restoration of the Mont-Saint-Michel's maritime characte

Experiments of helicopter ditching

International audienc